This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Objectives of Proposed Research: 1. Calibrate tissue 15N enrichment to lean mass use in torpid S. parryii that are either thermoneutral (Ta = +2[unreadable]C) or thermoregulating (Ta = -10[unreadable]C). 2. Elucidate and quantify patterns of expression of key metabolic genes of torpid S. parryii that are either thermoneutral (+2[unreadable]C) or thermoregulating (-10[unreadable]C). 3. Describe the energetics, substrate selection and limits to hibernation at extreme low Ta. 4. Correlate pre-hibernation body condition and hibernacula temperatures to overwinter changes in body condition, phenology, stable isotope signatures and components to fitness in natural populations. Given the extreme plasticity of their metabolism and body temperature, hibernators have been adopted as a model species for a number of human disease and injury states, including heart disease, ischemia, Alzheimer's, and traumatic head injury. Thus, results from the laboratory portion of this research could have applied implications for biomedicine. Field studies will contribute significantly to understanding organismal responses to a changing arctic climate. Proposed work will address important questions in hibernation physiology with new, interdisciplinary approaches. It will contribute significantly to comparative physiology by establishing limits to hibernation eco-physiology and mechanisms that create these constraints;to stable isotope ecology by documenting tissue 15N enrichment in an extreme animal model of starvation;and to comparative genomics, by further developing the RT-PCR approach to transcriptomics in a new model organism for ecophysiology and biomedicine. The work will link unique physiological traits of S. parryii with field measurements of hibernacula temperatures to increase knowledge of adaptation to the Arctic, and will provide the power to predict how changes in global climate may affect the population dynamics of an important arctic species.